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بسم هللا الرحمن الرحيم

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Warning!

This is the first lecture in the gastrointestinal system and the first

lecture ever for Doctor Mohammed Al-Muhtaseb. As we know the

doctor gives a lot of information during his lecture, so the sheets will

be long & condensed … so please be patient and may Allah be with

us during this system & during the long journey of medicine

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In this lecture we will cover the following subjects:

A) General introduction to the gastrointestinal tract.

B) General features of the gastrointestinal tract.

C) Layers of the gastrointestinal tract organs.

D) Histopathology (very brief point).

E) Clinical problem (Peptic ulcer – briefly–).

F) Gastrointestinal tract function (in general).

G) Basic mucosal forms in the gastrointestinal tract.

H) The Oral Cavity: (Tongue & Salivary glands)

تسهيال للطالب وذلك ;ترتيب المعلومات هنا يختلف عن ترتيبها أثناء المحاضرة :مالحظة

.إن شاء هللا ةحاضرمع التأكيد على وجود جميع المعلومات التي وردت بالم.أثناء قراءة الشيت وذلك منعا لـ الـلبس, تعود على الكلمة التي يعود إليها الضمير { }أي كلمة بين .

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A) Introduction:

The Gastrointestinal tract consists of:

1) Gastrointestinal tube:

Starts from the oral cavity (Mouth) then we have the pharynx,

esophagus, stomach, small intestine, large intestine, and the anal canal.

So it {the tube} starts from Oral cavity and ends with anal canal.

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2) Association organs:

Examples on them:

1) Salivary glands; which opens in the oral cavity; like the Parotid gland ,

Submandibular gland , and the Sublingual gland .

2) Liver & Gallbladder found in the abdomen

3) Pancereas .

:: these are called the association organs of the Gastrointestinal tract ::

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B) General features of the Gastrointestinal tract :

Shape-function relationship:

There is a relationship between the shape of the cells & their function (Always

the anatomy is related to Physiology ) :

Examples:

o Esophagus Have Stratified Squamous non keratinized epithelium

cells So it has Protective function.

o Stomach Have Simple columnar Epithelium, and we'll find that it is

rich in Glands (Tubular glands) So its function is Secretion &

Digestion.

o Colon Its function is Absorption & Formation of Feces So you'll

find that Lining Epithelium is rich in goblet cells ; which { goblet cells }

secrete Mucous for lubrication as a result of absorption of water, hard

masses resulting in friction with Mucosa . Also it {colon} is rich in tubular

glands for secretion.

:: from that { the three mentioned points } we can see that there is a relation

between the function & the type of cell :: .

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C) Layers of the GIT organs :

If we take any cross section from the GIT , we'll find that it consists of 4 layers

as following < starting from inside > :

Layer#1 = Mucosa.

Layer#2 = Submucosa.

Layer#3 = Muscular layer.

Layer#4 = Serosa or Adventitia

*Note: these layers vary from organ to another.

1- Mucosa (the first layer ):

Consists of 3 sub layers :

A) The Lining Epithelium:

As we said we have simple columnar epithelium in the stomach & duodenum

, stratified squamous non keratinized in esophagus and oral cavity , goblet

cells in colon (large intestine) for lubrication because there will be absorption

of water and formation of feces .

B) Lamina propria :

It is loose connective tissue , rich in glands(especially in stomach for digestion

purposes) , blood vessels , lymphatic's( the more distally we go in the GIT ,

lymphatic nodules increases for Immunity purposes ; because the food we

ingest may have bacteria( contamination) .

C) Musclaris Mucosa :

Which is a smooth muscle with; Inner Circular (IC) layer, Outer Longtidual (OL)

layer . It<Muscalaris Mucosa> can be one or two very thin layers . It is

responsible for the changes in the shape of mucosa or its motility.

:: End of the first layer - MUCOSA- ::

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2-SubMucosa ( the second layer ) :

Which is composed of Dense connective tissue; rich in blood vessels ,

lymphatics , and glands .

The glands of the Submucosa are found in two organs only in the GIT;

Esophagus & Duodenum ! . ( there is no gland in SubMucosa Elsewhere ).

Also there is Meissner's nerve plexus in the submucosa , and it is Autonomic (

sympathetic & parasympathetic ) .

:: end of the second layer –SubMucosa- ::

3-Muscalaris( the third layer ) : consisting of two layers ; Inner

circular & Outer longtidual .

Between the two layers we have plexus of nerves; called Myenteric ( or

Auerbach's) nerve plexus which is autonomic nervous system ( sympathetic &

parasympathetic) , it is responsible for the Peristalsis movement of the GIT .

The intestines are always in Peristaltic movement; the parasympathetic

Nervous System is responsible for it through the vagus nerve , which goes to

the Myenteric nerve plexus and finally to the smooth muscle , contracting it

and eventually Peristaltic movement .

Notes:

Always the parasympathetic is responsible for motility ( secretomotor

stimulation of the gland ) , it will stimulate the gland ; contracting it .

The sympathetic is always vasomotor for blood vessels; it will cause

vasoconstriction of the blood vessels leading to decrease in secretion

indirectly.

:: End of the third layer –MUSCLARIS - ::

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4-Serosa ( the 4th layer ) : If it's covered by peritoneum we name it

mesothelium layer . Mesothelium is simple squamous epithelium covering the

outer layer of the GI organs.

It is called Adventitia when the mesothelium is converted to connective

tissue.

It< Adventitia > is found in retroperitoneal organs within posterior abdominal

wall ( Duodenum , Gallbladder with liver ).

:: End of the 4th layer – Serosa- ::

:: Check the figure below and notice the 4 mentioned layers::

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D) Histopathology:

You have to know the normal histology to recognize the pathology.

In order to make diagnosis you have to compare between the specimen

(that is going to be tested) with the normal histology of that part (in

which the specimen is taken from ) .

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E) Clinical Problems :

Peptic ulcer: is the most important disease of the GIT; Most common site

is the duodenum (more accurate = first inch of duodenum) and it's called

dudenaulcer ) .

What causes peptic ulcer? The chyme of the stomach is acidic , and when it

reaches the first inch of the duodenum it will cause irritation to mucosa .

Normally, the duodenum is responsible for alkalization of the acidic chyme

, but sometimes excess of acidic chyme will cause irritation leading

eventually to duodenal ulcer .

Again the GIT Starts from the oral cavity ( Mouth ) then we have the

pharynx ,esophagus ,stomach, small intestine (Duodenum ,Geginum ,

ileum ) , large intestine( cecum . appendix ,ascending colon , transverse

colon ,descending colon , sigmoid colon ,and rectum) , and the anal

canal.

Association organs (Liver, gallbladder, pancreas) have different

histology. (To be discussed later Enshallah ) .

F) GIT function (in general):

Why we are blessed by the grace of GIT?

Because whenever we eat there will be digestion, and after digestion;

absorption will occur, and all the absorptive material will go by portal vein

to the liver, then feces will be formed accumulating in rectum and then

Defecation through the anal canal.

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Note: in Biochemical terms; Digestion: is changing complicated

materials into simple absorptive material.

Examples on that < the note > :

1) Carbohydrate (complicated-_-) will be digested to Simple glucose

(simple absorptive material^_^).

2) Proteins (complicated-_-) will be digested to Amino Acids (simple

absorptive material ^_^).

3) Fats (complicated -_-) will be digested to Fatty acids (simple

absorptive material ^_^).

They < simple absorptive material > will be absorbed and then go through

portal vein to the liver.

They go to the liver; because the function of the liver is store Glycogen,

Synthesis of enzymes, Forming coagulative material, the production of bile or

bile salts which are important for digestion, synthesis of heparin.

:: you can clearly realize that the liver have many important function , that’s

why we will take it in details Enshallah :: .

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G) Basic mucosal forms in the GIT:

We always relate function with structure. Examples:

1) If we look at the mucosa for example we may see that the function is

protection ( as in Esophagus and oral mucosa ) and the lining epithelium

is stratified squamous non keratinized .

As long as you're eating you can bite your mucosa leading to bleeding,

but after 6 hours there will be complete healing because stratified

squamous is characterized by Mitosis of cells! , so it will regenerate the

cells continuously.

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2) If we look at mucosa of stomach, we'll see the tubular glands that are

designed for secretory function, so the function of the stomach is

digestion, and the glands are responsible for secretion.

3) Absorptive : Small intestine ; especially the duodenum which

contains Brunners glands found in submucosa ; it helps in alkaline

secretion .

4) Protective/Absorptive : first inch of deudenum neutralizes the

acidic chyme of stomach. Also the colon may be absorptive for water,

protective in formation of feces.

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H) The Oral Cavity:

Consists of Tongue (for glutination) , Gums(Gingival) which contains the

sockets of teeth , Teeth ( for grinding of food) .

The oral cavity is rich in minor salivary glands; for moistestiring of the

food making the polus which will be swallowed.

Also there is opening (ducts) for the large salivary glands, which are

important for mucous and serous secretion.

As mentioned saliva is very important for; moisistring of food so we can

swallow it , giving us the ability to speak and making us happy .

Dryness of the mouth will lead to inflammations (stomatitis) because of

bacteria in the oral cavity replicate in dry environment leading to making

it pathogens , also loss of the ability to swallow.

Note: Large salivary gland are: Parotid , Submandibular , Sublingual glands

,1-1.5 liters of saliva are secreted daily.

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Generally the lining epithelium in the oral cavity is Stratified squamous

non-keratinized epithelium; but in the floor of the mouth it is

connected with loose connective tissue.

In the gums it < lining epithelium > is connected by dense connective

tissue, the same goes for the hard palate periosteum.

The type of epithelium can be changed; converting from non-

keratinized to para-keratinized. So if friction occurred to it, it will not

become keratinized but para-keratinized!

Para-Keratinized epithelium can be found in Gingiva , hard palate ,

and dorsum of the tongue .It is due to injury with digestion and it will

not reverse to non-keratinized nor keratinized .

TONGUE: ( check the figure below )

Is composed of two half's; right & left half, separated by midsagital line.

Since it's two half's there will be two muscles groups (one in each half) that

are the same.

Also it is divided into: Anterior 2/3 & Posterior 1/3.

Midsagital line

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The posterior third is lymphatic structure (consists of lymphatic tissue) &

no taste buds.

Anterior two thirds contain taste buds but no lymphatic nodules.

Circumvallate papillae, fungiform papillae, filiform papillae: they are

lingual papillae that contain taste buds, and they are found on the anterior

aspect of the tongue . The cells responsible for sensation of taste (sweet ,

bitter , salt ,….) are found on the dorsum surface of the anterior two thirds

of the tongue which contain the taste buds .

The dorsum surface of the anterior two thirds of the tongue is lined by

Stratified squamous para-Keratinized because the dorsum is always at

risk of injury .While the lower surface is stratified squamous non

keratinized epithelium.

The tongue is muscular organ contains skeletal striated muscles in

different directions.

Taste buds : in the middle of it we have Taste cells ; which will take the

dissolving material and convert it to taste impulses ( special signals(taste

impulses) for tasting that will be transmitted through the nerve responsible

for tasting ;which is afferent nerve fiber ; which is a part of corda tymapni

of the facial nerve , then it < special signals > will reach the tasting centers

in the brain resulting in taste recognition ^_^ ) .

Around it < tasting cell > there is supporting cells, also we can see

lymphatic nodule especially in the posterior third of tongue.

:: check the figure below to see the taste cells ::

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Remember: Anterior 2/3 stratified squamous para-keratinized

epithelium.

There is a gland around the taste buds called Von Ebner's gland; which

secrete serous on the groove around the lingual papillae, dissolving

materials, to feel the taste sensation. ( the pointed at structure below)

:: end of the tongue ::

Taste cells))

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Salivary gland:

We have minor glands & three large pairs of glands. Minor

salivary glands secrete mucous mostly , when it <minor SG> is

found on the lip it's called Labial salivary gland , if it's found on

palate it's called palatial salivary gland , if it's found on tongue

it's called lingual salivary gland .

The three pairs ; we have the Parotid ( related to ramus of

mandible from outside ) , Submandibular (related to sub

mandibular fossa of the mandible ) , Sublingual ( related

sublingual fossa of the mandible ) .

Mylohyoid muscle separates Submandibular gland from

Sublingual gland.

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These glands < the large ones > some of its secretions is

mucous, and some of it is serous secretion. Serous means; amy

lysoenzymes & Immunoglobulin for killing bacteria. Some of

them will secrete only one type of secretions, others are mixed

glands (serous and mucous ) .

Note:

Parotid gland only serous secretion.

Submandibular gland Mixed!

Sublingual gland mostly mucous secretion.

Each one of the large glands has its own duct ; which opens in

the oral cavity. Example : Parotid duct open on the upper

second molar tooth , so if it <the duct > was obstructed ;

Swelling of parotid gland will occur , causing severe pain (

when the patient see food , his gland will be stimulated

,secretion will start , finally swelling ) .

Any gland of the large ones ;is surrounded by a capsule of

connective tissue ; except for the Parotid gland which has two

capsules , and from here any swelling in it will cause severe

pain ( because there will be no enlargement , but there will be

pressure on the structure of the gland ).

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The capsule is connective tissue, usually sends septa between

the lobes & lobules of the gland,so the gland is divided into

lobes & lobules by connective tissue septa . The septa have two

functions :

1) Contains blood vessels, lymphatics, Nerves.

2) Contains Large ducts; they act as passageway (for

the secretions) to oral cavity.

Accumulation of secretory cells is called Acini . (6-8 secretory

cells ) will form Acinus , group of Acinus is called Acini .

Acini can be serous acini or mucous acini or mixed depending

on the gland type.

Lumen is where the secretions accumulate , and from it ,small

duct will start .After small duct appearance, it will become

intercalated ducts , and when it enlarges it will be Striated

ducts .when it reaches between the lobes it's called interlobar

duct , and it is a large duct .

Myoepitheilial cells: between the basement membrane of the

acini and the acini cells , called myo ; because it contain

myofibirs , it's function is to squeeze the gland , push the

secretion to the lumen , eventually to the duct .

Serous acini is smaller than Mucous acini. The nuclei of the

Mucous acini is flattend and basal, while in serous acini they

are rounded and below center (near the base).

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Zymogens granules are found in the apex of the serous acini

making it acidophilic & the base is basophilic , while the

mucous acini is filled with mucous secretion so when doing

laboratory preparation to it , it will give foamy appearance (

vacuole ) .

Intercalated duct is the smallest duct, consisting of 5-8 simple

cuboidal cells .While the striated duct is a larger duct, named

striated because there is elongated fold of the basement

membrane , and the presence of mitochondria there

(elongated fold) .

Interlobal duct ; starts as simple cuboidal then it become

startified cuboidal startified columnar stratified

squamous ( when it reaches the opening of the oral cavity ) ,

blood vessels & lymphatics accompanies the iterlobal duct .

:: all Previously mentioned stuff about the salivary glands & their

cells are illustrated in the figure below ::

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In the submandbibular gland, the secretion is mixed therefore

we can find the Serous Demilunes = capping of serous over

mucous acini .

( check the figure below to see Serous Demilunes"S ) .

In basket cells (myoepitheleal duct), mucous is more than

serous.

Submandibular duct has complicated duct.

The Sublingual duct is very minimal and its secretion is mostly

mucous but serous demilune could be found.

Minor salivary are numerous like labial , palatal . Most of its

secretion is mucous. in the tongue we have von ebner's gland

and it secretes serous only which contains enzymes, IG and

aggregation of lymphocytes and opens into vallate papillae,

:: End of Salivary glands ::

:: THE END::

… لغوي أو علميبعتذر عن أي خطأ …

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عالء الدين دحبور | زميلكم